A torque measuring system has been known which is of the type having a pair of magnetically anisotropic portions formed on the periphery of a torque transmission shaft such that when a torque is applied to the shaft, a pair of sensing coils arranged adjacent the magnetically anisotropic portions detect a change in the permeability of the portions and issue detection signals individually so that on the basis of the difference between the two signals the magnitude of the torque acting on the shaft is converted into an electric signal.
With such prior-art torque measuring system, the problem is that sensor outputs in such a condition that no torque is acting on the shaft, that is, zero-point outputs, and/or detection sensitivity of the sensor are subject to variation under the influence of the ambient temperature condition and various other factors.
Among possible causes of such variation in sensor output are unbalance of magnetically anisotropic portions formed on the shaft at opposite locations, unbalance in characteristics of shields disposed at opposite locations, and unbalance in characteristics of bobbins and coils arranged at opposite locations. For example, where the magnetically anisotropic portions are formed by knurl groove rolling and subsequently subjecting the worked knurl grooves to heat treatment and shot peening, the unbalance of the magnetically anisotropic portions may be attributable to unbalance of the rolled grooves in respect of groove depth and width, unbalance of heat treatment, and/or unbalance of shot peening operation.
As a measure to correct such variation in sensor outputs, it has been known to provide correction resistors such that when there occurs a change the correction resistors may be replaced through soldering, or selectively used through a dip switch control, or adjusted by means of variable resistors, as described in, for example, Japanese Patent Application No. 3-311137.
However, such prior art correction practice has involved the problem that correction is carried out by manually replacing and/or adjusting electronic parts, which often results in inaccurate correction and which is time consuming.